The treatment, dubbed "chemoimmunotherapy", involved low doses of the drug oxaliplatin which has a unique ability to activate cancer-killing immune cells. Equally important to the treatment was removing or blocking immune system cells that put a brake on the body's defences.

Each year in the UK around 41,000 men are diagnosed with prostate cancer and 11,000 die from the disease.

The immunosuppressive "B-cells" are especially abundant in the tumours of men who have advanced and spreading prostate cancer.

Such cells can render conventional therapies ineffective and allowing tumours to grow unchecked.

Because of immunosuppression, advanced and aggressive prostate cancer does not typically respond to chemotherapy.

US lead scientist Dr Shabnam Shalapour, from the University of California at San Diego, said the new approach should now be tested clinically.

B-cells also undermine the effectiveness of promising new drugs called checkpoint inhibitors which "unmask" cancer cells allowing them to be recognised by the immune system.

While early treatment is often highly successful, there are few options for men with aggressive drug-resistant prostate cancer that has started to spread.

B-cells play a number of vital immune system roles, including the production of antibodies. Sometimes they also signal the immune system to slow down when it is getting overheated.

In the context of cancer, this can have undesirable consequences, researchers writing in the journal Nature said.

Co-author Professor Michael Karin, also from the University of California at San Diego, said there may be implications for the treatment of other types of cancer.

He said: "Similar immunosuppressive B-cells can be detected in other human cancers.

"This indicates that B-cell-mediated immunosuppression might be the reason several other cancers are also unresponsive to checkpoint inhibitors, raising the hope that chemoimmunotherapy will have broader applications for many cancer types."

Earlier this week Canadian research found prostate cancer sufferers treated with tiny radioactive implants are twice as likely to be cancer-free as those given conventional therapy after five years.

Scientists behind the first ever trial comparing low-dose brachytherapy with any other form of radiation said there was a “large advantage” to the implants, in terms of survival.

However, the research found that men given the treatment – which involves permanently implanted radioactive “seeds” - suffered more severe side-effects, such as urinary problems.